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Biology 12 E. McIntyre

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Primarily energy sources and structural compounds and signaling molecules. ... fatty acids are joined with ester bonds (a condensation reaction involving ... – PowerPoint PPT presentation

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Title: Biology 12 E. McIntyre


1
Biology 12 E. McIntyre
  • Biological Macromolecules
  • Lipids
  • See Chap 1.2 in your text Biology 12

2
General Characteristics
  • All Lipids are hydrophobic. Consist of carbon,
    hydrogen and oxygen
  • Contain fewer polar O-H bonds and more non-polar
    C-H bonds than carbohydrates.
  • includes fats and oils, waxes, phospholipids,
    steroids, and some other related compounds.
  • Primarily energy sources and structural compounds
    and signaling molecules.
  • Large number of bonded hydrogens - therefore
    release a larger amount of energy than other
    organic compounds. Fats yield 9kcal/gm,
    carbohydrates 4kcal/gm

3
Types of Lipids
  • Lipids with fatty acids
  • Triglycerides (Fats and oils)
  • Phospholipids
  • Waxes
  • Lipids without fatty acids
  • Steroids

4
Triglycerides

Hydroxyl groups
  • Triglycerides (fats and oils)
  • Composed of three fatty acids joined to a
    glycerol molecule.
  • Glycerol is a three carbon molecule with hydroxyl
    groups on each carbon.
  • Fatty acids - long hydrocarbon chains with
    terminal carboxyl (COOH) group.

5
Triglycerides
  • Triglycerides are synthesized via condensation
    reactions.
  • Glycerol fatty acids are joined with ester
    bonds (a condensation reaction involving hydroxyl
    and carboxyl groups)

6
Types of Lipids
  • The main distinction between fats and oils is
    whether theyre solid or liquid at room
    temperature
  • Fats
  • mostly from animal sources
  • triglycerides containing saturated fatty acids
    (e.g. butter is solid at room temperature)
  • Oils
  • mostly from plant sources
  • triglycerides with unsaturated fatty acids (e.g.
    corn oil is liquid at room temperature)

7
Fatty Acids
  • Structure of Fatty Acids
  • all fatty acids have long hydrocarbon chains with
    terminal carboxyl (COOH) group
  • The tail of a fatty acid is a long hydrocarbon
    chain, making it hydrophobic.
  • Typically 12-18 carbon atoms (even number)
  • Saturated fatty acids have no double bonds
    between their carbon atoms
  • Unsaturated fatty acids have double bonds in the
    carbon chain

8
Saturated and Unsaturated Fatty Acids
  • Saturated Fatty acids
  • The terms saturated, mono-unsaturated, and
    poly-unsaturated refer to the number of hydrogen
    attached to the hydrocarbon tails of the fatty
    acids as compared to the number of double bonds
    between carbon atoms in the tail.
  • Saturated fats have all single bonds between the
    carbons in their fatty acid tails, thus all the
    carbons are also bonded to the maximum number of
    hydrogen possiblemaximum possible amount of
    hydrogen ? saturated fats.
  • The hydrocarbon chains in these fatty acids are,
    thus, fairly straight and can pack closely
    together. There are strong attractions between
    the fatty acids in triglycerides with saturated
    fatty acids. These fats are solid at room
    temperature.

9
Saturated and Unsaturated Fatty Acids
  • Unsaturated Fatty acids
  • Oils have some double bonds between some of the
    carbons in the hydrocarbon tail, causing bends or
    kinks in the shape of the molecules.
  • Because some of the carbons share double bonds,
    theyre not bonded to as many hydrogen as they
    could if they werent double bonded to each
    other. These oils are called unsaturated fats.
  • Because of the kinks in the hydrocarbon tails,
    unsaturated fats cant pack as closely together,
    making them liquid at room temperature.
  • unsaturated fats are healthier
  • than the saturated ones.

10
Saturated and Unsaturated Fatty Acids
  • Hydrogenated vegetable oil (as in shortening and
    commercial peanut butters where a solid
    consistency is sought) started out as good
    unsaturated oil. However, this commercial product
    has had all the double bonds artificially broken
    and hydrogen artificially added (in a chemistry
    lab-type setting) to turn it into saturated fat
    that bears no resemblance to the original oil
    from which it came (so it will be solid at room
    temperature).

11
Cis and Trans Bonds
  • In unsaturated fatty acids, there are two ways
    the pieces of the hydrocarbon tail can be
    arranged around a CC double bond.
  • In cis bonds, the two hydrogens on either side of
    the double bond are either both up or both
    down, (both are on the same side of the
    molecule).
  • In trans bonds, the two hydrogens are on opposite
    sides of the double bond, One is up and one is
    down.

12
Cis and Trans Bonds
  • Naturally-occurring unsaturated vegetable oils
    have almost all cis bonds, but using oil for
    frying causes some of the cis bonds to convert to
    trans bonds. If oil is used only once like when
    you fry an egg, only a few of the bonds do this
    so its not too bad. However, if oil is
    constantly reused, like in fast food French fry
    machines, more and more of the cis bonds are
    changed to trans until significant numbers of
    fatty acids with trans bonds build up.

13
Cis and Trans Bonds
  • Fatty acids with trans bonds are carcinogenic, or
    cancer-causing. The levels of trans fatty acids
    in highly-processed, lipid-containing products
    such as margarine are quite high.
  • Cis fats exist naturally and, because the
    hydrogen atoms are crowded on one side of the
    molecule, they bend, allowing other chemicals and
    enzymes to bind to them.
  • Trans fats do not exist naturally, with a very
    few exceptions. Because the structure is
    uncrowded, they do not bend and so other
    molecules and enzymes find it more difficult to
    bind to them.
  • In fact, it is the very fact that they are
    straight that allows trans fats to solidify at
    room temperature. Natural, cis fats are curved
    and so can't pack into a crystal formation at
    normal temperatures. Trans fats, on the other
    hand, are straight and CAN pack into a crystal
    formation, which allows them to solidify at room
    temperature.

14
Stop Think
  • How would the melting point of stearic acid
    compare to the melting points of oleic acid and
    linoleic acid? Assign the melting points of
    17C, 13C, and 69C to the correct fatty acid.
    Explain.
  • stearic acid (18 C) saturated
  • oleic acid (18 C) one double bond
  • linoleic acid (18 C) two double bonds

15
Solution to Stop Think
  • Stearic acid is saturated and would have a
    higher melting point than the unsaturated fatty
    acids. Because linoleic has two double bonds, it
    would have a lower mp than oleic acid, which has
    one double bond.
  • stearic acid mp 69C
  • oleic acid mp 13C
  • linoleic acid mp -17C

16
Stop Think
  • Identify each fatty acid as a
  • trans unsaturated fatty acid
  • cis unsaturated fatty
  • saturated fatty acid

Oleic acid Elaidic acid Stearic acid
17
Solution to Stop Think
Oleic acid Elaidic acid Stearic acid
Oleic acid is a cis unsaturated fatty acid that comprises 5580 of olive oil. Elaidic acid is a trans unsaturated fatty acid often found in partially hydrogenated vegetable oils. Stearic acid is a saturated fatty acid found in animal fats and as the intended product in hydrogenation.


18
Stop Think
  • Which two fatty acids are isomers?

19
Solution to Stop Think
  • Which two fatty acids are isomers?

20
Types of Lipids
  • Phospholipids - two fatty acids attached to
    phosphate group
  • phosphate heads are hydrophilic (water soluble)
    but tails are hydrophobic (water insoluble).
  • spontaneously form miscelles in water.
  • very important because they form biological
    membranes

21
Membrane Structure
  • Phospholipid bilayer
  • Hydrophillic heads in contact with aqueous
    environment
  • Hydrophobic tails reside in interior of bilayer
  • Cholesterol is a structural component
  • Proteins
  • Integral
  • Peripheral
  • Lipid anchored
  • Dynamic structure

22
Stop Think
  • Sketch the arrangement of miscelles in a oily
    environment

23
Solution to Stop Think
24
Steroids (Sterols)
  • Compact hydrophobic molecules containing four
    fused hydrocarbon rings and several different
    functional groups
  • Examples
  • Cholesterol-precursor
  • to sex hormones and
  • vitamin D
  • Sex hormones

25
Steroids (Sterols)
  • Cholesterol
  • High concentrations of cholesterol in the
    bloodstream and a diet rich in saturated fats
    have been linked to the development of
    atherosclerosis, a condition in which fatty
    deposits, called plaque, form on the inner lining
    of blood vessels, blocking the flow of blood to
    tissues. Deprived of oxygen and nutrients, the
    cells of the tissues die.

26
Steroids (Sterols)
  • Cholesterol
  • Vitamin D is formed by the action of UV light in
    sunlight on cholesterol molecules that have
    risen to near the surface of the skin.
  • Many medical journals state that people not
    shower immediately after being in the sun, but
    wait at least ½ hour for the new Vitamin D to be
    absorbed deeper into the skin.
  • Our cell membranes contain a lot of cholesterol
    (in between the phospholipids).

27
Steroids (Sterols)
  • Cholesterol
  • Cholesterol is not the bad guy. Its how it is
    packaged.
  • LDL is the bad cholesterol
  • HDL is the good cholesterol.

28
Stop Think
  • Examine the cholesterol and phospholipid
    molecules. Predict how the cholesterol molecules
    are oriented among the phospholipids of a
    membrane.

29
Solution to Stop Think
  • Cholesterol is an amphipathic molecule, meaning,
    like phospholipids, it contains a hydrophilic and
    a hydrophobic portion. Cholesterol's hydroxyl (OH)

group aligns with the phosphate heads of the
phospholipids. The remaining portion of it tucks
into the fatty acid portion of the membrane.
30
Soaps
  • The tail of a fatty acid is a long hydrocarbon
    chain, making it hydrophobic. The head of the
    molecule is a carboxyl group which is
    hydrophilic. Fatty acids are the main component
    of soap, where their tails are soluble in oily
    dirt and their heads

are soluble in water to emulsify and wash away
the oily dirt. However, when the head end is
attached to glycerol to form a fat, that whole
molecule is hydrophobic.
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